Liquid crystal display device

ABSTRACT

According to one embodiment, a liquid crystal display device includes an array substrate including a first color filter configured to transmit light in a first wavelength range, a second color filter configured to transmit light in a second wavelength range of greater wavelengths than the first wavelength range, a first switching element disposed above the second color filter, a second switching element disposed above the second color filter, a first pixel electrode which is electrically connected to the first switching element and is located above the first color filter, and a second pixel electrode which is electrically connected to the second switching element and is located above the second color filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/357,196 filed Jan. 24, 2012, and is based upon and claims the benefitof priority from prior Japanese Patent Application No. 2011-158425,filed Jul. 19, 2011, the entire contents of each of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a liquid crystaldisplay device.

BACKGROUND

In recent years, flat-panel display devices have been vigorouslydeveloped. By virtue of such advantageous features as light weight,small thickness and low power consumption, special attention has beenpaid to liquid crystal display devices among others. In particular, inactive matrix liquid crystal devices in which thin-film transistors(TFTs) are incorporated in respective pixels as switching elements,there is known such a configuration that a transmissive liquid crystaldisplay panel and a backlight are combined.

In a structure wherein a top-gate-type polysilicon TFT including apolysilicon semiconductor layer is applied as a switching element, aproblem arises with an increase of OFF current due to an increase inluminance of a backlight. Specifically, a drain current of a TFTincreases by the absorption of backlight in the polysiliconsemiconductor layer. The increase in drain current conspicuously occursin the state in which the TFT is in the OFF state, and such a draincurrent is called “photo-leakage current”. In recent years, to meet ademand for a higher luminance of the screen, there is a tendency toincrease the luminance of backlight. Consequently, there is concern thatthe display quality is adversely affected by, e.g. crosstalk or flickerdue to the increase in photo-leakage current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view which schematically illustrates a structure of a liquidcrystal display device according to an embodiment.

FIG. 2 is a view which schematically illustrates a structure and anequivalent circuit of a liquid crystal display panel shown in FIG. 1.

FIG. 3 is a view which schematically shows a cross-sectional structureof the liquid crystal display panel shown in FIG. 2.

FIG. 4 is a cross-sectional view which schematically shows a dielectricfilm multilayer with a 5-layer structure, which constitutes a firstcolor filter, a second color filter and a third color filter.

FIG. 5 is a cross-sectional view which schematically shows a dielectricfilm multilayer with a 7-layer structure, which constitutes the firstcolor filter, second color filter and third color filter.

FIG. 6 is a cross-sectional view which schematically shows a dielectricfilm multilayer with a 9-layer structure, which constitutes the firstcolor filter, second color filter and third color filter.

FIG. 7 is a graph showing an example of a relationship between a lightemission spectrum of a backlight and reflection spectra of color filtersof the embodiment.

FIG. 8 is a graph showing a relationship between a photo-leakage amountin a switching element of each of pixels and the number of layers of thedielectric film multilayer.

DETAILED DESCRIPTION

In general, according to one embodiment, a liquid crystal display deviceincludes an array substrate including a first color filter configured totransmit light in a first wavelength range; a second color filterconfigured to transmit light in a second wavelength range of greaterwavelengths than the first wavelength range; a first switching elementdisposed above the second color filter; a second switching elementdisposed above the second color filter; a first pixel electrode which iselectrically connected to the first switching element and is locatedabove the first color filter; and a second pixel electrode which iselectrically connected to the second switching element and is locatedabove the second color filter.

According to another embodiment, a liquid crystal display deviceincludes an array substrate including an insulative substrate; a firstsemi-transmissive layer disposed on the insulative substrate; a firsttransmissive layer with a first film thickness, a second transmissivelayer with a second film thickness which is different from the firstfilm thickness, and a third transmissive layer with a third filmthickness which is different from the first film thickness and thesecond film thickness, the first transmissive layer, the secondtransmissive layer and the third transmissive layer being disposed onthe first semi-transmissive layer; a second semi-transmissive layerdisposed on the first transmissive layer to constitute a first colorfilter configured to transmit light in a first wavelength range,disposed on the second transmissive layer to constitute a second colorfilter configured to transmit light in a second wavelength range ofgreater wavelengths than the first wavelength range, and disposed on thethird transmissive layer to constitute a third color filter configuredto transmit light in a third wavelength range of greater wavelengthsthan the second wavelength range; a first switching element, a secondswitching element and a third switching element, which are disposed onthe second semi-transmissive layer which constitutes the second colorfilter or the third color filter; a first pixel electrode which iselectrically connected to the first switching element and is locatedabove the first color filter; a second pixel electrode which iselectrically connected to the second switching element and is locatedabove the second color filter; and a third pixel electrode which iselectrically connected to the third switching element and is locatedabove the third color filter.

According to another embodiment, a liquid crystal display deviceincludes an array substrate including an insulative substrate, adielectric film multilayer formed on the insulative substrate andconfigured to reflect light of a blue wavelength to the insulativesubstrate side, a top-gate-type thin-film transistor including a siliconsemiconductor layer disposed on the dielectric film multilayer, and apixel electrode electrically connected to the thin-film transistor; acounter-substrate disposed to be opposed to the array substrate; and aliquid crystal layer held between the array substrate and thecounter-substrate.

Embodiments will now be described in detail with reference to theaccompanying drawings. In the drawings, structural elements having thesame or similar functions are denoted by like reference numerals, and anoverlapping description is omitted.

FIG. 1 is a view which schematically illustrates a structure of a liquidcrystal display device according to an embodiment.

Specifically, the liquid crystal display device 1 includes anactive-matrix-type transmissive liquid crystal display panel LPN, adriving IC chip 2 and a flexible wiring board 3 which are connected tothe liquid crystal display panel LPN, and a backlight 4 whichilluminates the liquid crystal display panel LPN.

The liquid crystal display panel LPN includes an array substrate AR, acounter-substrate CT which is disposed to be opposed to the arraysubstrate AR, and a liquid crystal layer which is held between the arraysubstrate AR and the counter-substrate CT. The liquid crystal displaypanel LPN includes an active area ACT which displays an image. Theactive area ACT is composed of a plurality of pixels PX which arearrayed in a matrix of m×n (m and n are positive integers).

The backlight 4 is disposed on the back side of the array substrate AR.As the backlight 4, use may be made of either a backlight including alight-emitting diode (LED) as a light source, or a backlight including acold cathode fluorescent lamp (CCFL) as a light source. A description ofthe detailed structure of the backlight 4 is omitted.

FIG. 2 is a view which schematically shows a structure and an equivalentcircuit of the liquid crystal display panel LPN shown in FIG. 1.

The array substrate AR includes, in the active area ACT, a plurality ofgate lines G (G1 to Gn), a plurality of storage capacitance lines C (C1to Cn), and a plurality of source lines S (S1 to Sm). Each of the gatelines G is led out of the active area ACT and is connected to a gatedriver GD. Each of the source lines S is led out of the active area ACTand is connected to a source driver SD.

Each of the pixels PX includes a switching element SW, a pixel electrodePE and a counter-electrode CE. The switching element SW is electricallyconnected to the gate line G and source line S. The pixel electrode PEis electrically connected to the switching element SW. Thecounter-electrode CE is formed common to plural pixel electrodes PE viaa liquid crystal layer LQ. The counter-electrode CE is electricallyconnected to a power supply module VS.

In the present embodiment, the switching element SW and pixel electrodesPE are provided on the array substrate AR. On the other hand, thecounter-electrode CE may be provided on the array substrate AR, or onthe counter-substrate CT. In the liquid crystal display panel LPN thatis configured such that the counter-electrode CE, as well as the pixelelectrodes PE, is disposed on the array substrate AR, liquid crystalmolecules, which constitute the liquid crystal layer LQ, are switched bymainly using a lateral electric field which is produced between thepixel electrodes PE and the counter-electrode CE. In the liquid crystaldisplay panel LPN that is configured such that the counter-electrode CEis disposed on the counter-substrate CT, the liquid crystal molecules,which constitute the liquid crystal layer LQ, are switched by mainlyusing a vertical electric field or an oblique electric field, which isproduced between the pixel electrodes PE and the counter-electrode CE.

FIG. 3 is a view which schematically shows a cross-sectional structureof the liquid crystal display panel LPN shown in FIG. 2. FIG. 3 showscross-sectional structures of a first pixel PX1 which displays blue, asecond pixel PX2 which displays green, and a third pixel PX3 whichdisplays red.

Specifically, the first pixel PX1 includes a first color filter CF1, afirst switching element SW1 and a first pixel electrode PE1. The secondpixel PX2 includes a second color filter CF2, a second switching elementSW2 and a second pixel electrode PE2. The third pixel PX3 includes athird color filter CF3, a third switching element SW3 and a third pixelelectrode PE3.

The array substrate AR is formed by using a first insulative substrate10 with light transmissivity, such as a glass substrate. The first colorfilter CF1, second color filter CF2 and third color filter CF3 aredisposed on the first insulative substrate 10. The first color filterCF1 transmits light of a first wavelength range (e.g. wavelength rangeof 400 nm to 500 nm) which is a blue wavelength range. The second colorfilter CF2 transmits light of a second wavelength range (e.g. wavelengthrange of 500 nm to 580 nm) which is a green wavelength range and is arange of greater wavelengths than the first wavelength range. The thirdcolor filter CF3 transmits light of a third wavelength range (e.g.wavelength range of 580 nm to 700 nm) which is a red wavelength rangeand is a range of greater wavelengths than the second wavelength range.

The first color filter CF1, second color filter CF2 and third colorfilter CF3 mainly reflect light of wavelengths, which are other than thelight of wavelengths that is transmitted. The first color filter CF1 hasa higher reflectance in the second wavelength range and the thirdwavelength range than in the first wavelength range. The second colorfilter CF2 has a higher reflectance in the first wavelength range andthe third wavelength range than in the second wavelength range. Thethird color filter CF3 has a higher reflectance in the first wavelengthrange and the second wavelength range than in the third wavelengthrange.

As will be described later in detail, the backlight 4, which is appliedto the embodiment, has a light emission spectrum having a light emissionpeak (about 450 nm) in the first wavelength range. The second colorfilter CF2 and third color filter CF3 have such reflectancecharacteristics that the reflectance in the neighborhood of 450 nm,which is the light emission peak of the backlight 4, is higher than thereflectance in the second wavelength range and third wavelength range.

In the example illustrated, the first color filter CF1 is disposed inaccordance with the first pixel PX1, except under the first switchingelement SW1. The second color filter CF2 is disposed in accordance withthe second pixel PX2, except under the second switching element SW2. Thethird color filter CF3 is disposed in accordance with the third pixelPX3. In addition, the third color filter CF3 is also disposed under thefirst switching element SW1, second switching element SW2 and thirdswitching element SW3. In the example illustrated, the third colorfilter CF3 is applied as the underlayer of the first switching elementSW1, second switching element SW2 and third switching element SW3.Alternatively, the second color filter CF2, which reflects light of thefirst wavelength range, may be applied.

As the first color filter CF1, second color filter CF2 and third colorfilter CF3, light-absorption-type filters (e.g. filters formed ofcolored resins) may be used. In the example illustrated, however,Fabry-Ferot-type filters, which make use of the principle of opticalinterference, are adopted. Specifically, the first color filter CF1,second color filter CF2 and third color filter CF3 are formed bystacking a plurality of thin films with different refractive indices,and include a first semi-transmissive layer 31 which is disposed on aninner surface 10A of the first insulative substrate 10, a secondsemi-transmissive layer 32 which is opposed to the firstsemi-transmissive layer 31, and a transmissive layer (or a spacer layer)33 which is disposed between the first semi-transmissive layer 31 andthe second semi-transmissive layer 32.

To be more specific, the first semi-transmissive layer 31 and the secondsemi-transmissive layer 32 are provided common to the first color filterCF1, second color filter CF2 and third color filter CF3. Each of thefirst semi-transmissive layer 31 and the second semi-transmissive layer32 may be a metal thin film formed of, silver (Ag) with a thickness onthe several-ten nm order, or may be a multilayer structure in which aplurality of dielectric films with different refractive indices arestacked. For example, each of the first semi-transmissive layer 31 andthe second semi-transmissive layer 32 can be formed by a multilayer inwhich a silicon nitride (SiN) layer and a silicon oxide (SiO₂) layer arealternately stacked. The number of stacked dielectric films of themultiplayer is two or more. However, as the number of layers increases,the number of fabrication steps increases and the manufacturing costincreases. It is thus desirable that the number of layers be set at fouror less.

The transmissive layer 33 is a single dielectric film, and can be formedof a silicon nitride layer or a silicon oxide layer. The transmissivelayer 33 includes a first transmissive layer 331, a second transmissivelayer 332 and a third transmissive layer 333, which have different filmthicknesses.

The first color filter CF1 includes the first transmissive layer 331with a first film thickness T1, as the transmissive layer 33 disposedbetween the first semi-transmissive layer 31 and secondsemi-transmissive layer 32. The second color filter CF2 includes thesecond transmissive layer 332 with a second film thickness T2, which isdifferent from the first film thickness T1, as the transmissive layer 33disposed between the first semi-transmissive layer 31 and secondsemi-transmissive layer 32. The third color filter CF3 includes thethird transmissive layer 333 with a third film thickness T3, which isdifferent from the first film thickness T1 and second film thickness T2,as the transmissive layer 33 disposed between the firstsemi-transmissive layer 31 and second semi-transmissive layer 32. Thefirst transmissive layer 331, second transmissive layer 332 and thirdtransmissive layer 333, although having different film thicknesses, aremutually continuous. In the example illustrated, the second filmthickness T2 is greater than the first film thickness T2, and the thirdfilm thickness T3 is less than the first film thickness T1.

The first switching element SW1, second switching element SW2 and thirdswitching element SW3 are all composed of top-gate-type thin-filmtransistors (TFTs), and have substantially the same structure. In thedescription below, the first switching element SW1 is described moreconcretely, and a description of the structure of each of the secondswitching element SW2 and third switching element SW3 is omitted.

Specifically, the first switching element SW1 includes a semiconductorlayer SC which is disposed on the third color filter CF3 (strictlyspeaking, on the second semi-transmissive layer 32). The siliconsemiconductor layer is formed of polysilicon, but there may be a case inwhich the silicon semiconductor layer is formed of amorphous silicon.The silicon semiconductor layer SC is covered with a first insulationfilm 11. The first insulation film 11 covers the first color filter CF1,second color filter CF2, and third color filter CF3.

A gate electrode WG of the first switching element SW1 is formed on thefirst insulation film 11 and is located immediately above the siliconsemiconductor layer SC. The gate electrode WG is electrically connectedto the gate line and is covered with a second insulation film 12. Thesecond insulation film 12 is also disposed on the first insulation film11.

A source electrode WS and a drain electrode WD of the first switchingelement SW1 are formed on the second insulation film 12. The sourceelectrode WS is electrically connected to the source line. The sourceelectrode WS and drain electrode WD are put in contact with the siliconsemiconductor layer SC via contact holes which penetrate the firstinsulation film 11 and second insulation film 12.

The first switching element SW1 having the above-described structure iscovered with a third insulation film 13. Similarly, the second switchingelement SW2 and third switching element SW3 are covered with the thirdinsulation film 13. The third insulation film 13 is also disposed on thesecond insulation film 12.

The first pixel electrode PE1 is formed on the third insulation film 13and is located above the first color filter CF1. The first pixelelectrode PE1 is electrically connected to the drain electrode WD of thefirst switching element SW1 via a contact hole which penetrates thethird insulation film 13.

Similarly, the second pixel electrode PE2 is formed on the thirdinsulation film 13 and is located above the second color filter CF2. Thesecond pixel electrode PE2 is electrically connected to the drainelectrode WD of the second switching element SW2. In addition,similarly, the third pixel electrode PE3 is formed on the thirdinsulation film 13 and is located above the third color filter CF3, andis electrically connected to the drain electrode WD of the thirdswitching element SW3.

The first pixel electrode PE1, second pixel electrode PE2 and thirdpixel electrode PE3 are formed of a light-transmissive, electricallyconductive material, such as indium tin oxide (ITO) or indium zinc oxide(IZO). These first pixel electrode PE1, second pixel electrode PE2 andthird pixel electrode PE3 are covered with a first alignment film AL1.

The counter-substrate CT is formed by using a second insulativesubstrate 20 having light transmissivity, such as a glass substrate. Thecounter-substrate CT includes a black matrix BM on an inner surface 20Aof the second insulative substrate 20, which is opposed to the arraysubstrate AR. The black matrix BM is formed so as to be opposed to thefirst switching element SW1, second switching element SW2 and thirdswitching element SW3, and wiring parts such as source lines, gatelines, and storage capacitance lines.

In the example illustrated, the counter-substrate CT includes a firstcolor layer CF11, a second color layer CF12 and a third color layer CF13on the inner surface 20A of the second insulative substrate 20, but thefirst color layer CF11, second color layer CF12 and third color layerCF13 may be dispensed with. The first color layer CF11 is formed of acolor resin (e.g. blue resin) which transmits light of the firstwavelength range. The second color layer CF12 is formed of a color resin(e.g. green resin) which transmits light of the second wavelength range.The third color layer CF13 is formed of a color resin (e.g. red resin)which transmits light of the third wavelength range.

In addition, in the example illustrated, the counter-electrode CTincludes the counter-electrode CE on those surfaces of the first colorlayer CF11, second color layer CF12 and third color layer CF13, whichare opposed to the array substrate AR. The counter-electrode CE, asdescribed above, may be provided on the array substrate AR. Thecounter-electrode CE is formed of a light-transmissive, electricallyconductive material, such as ITO or IZO. That surface of thecounter-electrode CT, which is opposed to the array substrate AR, iscovered with a second alignment film AL2.

The above-described array substrate AR and counter-substrate CT aredisposed such that their first alignment film AL1 and second alignmentfilm AL2 are opposed to each other. In this case, a predetermined cellgap, for example, a cell gap of 2 to 7 μm, is created between the arraysubstrate AR and the counter-substrate CT by columnar spacers which areformed of, e.g. a resin material so as to be integral to one of thearray substrate AR and counter-substrate CT. The liquid crystal layer LQis held in the cell gap which is created between the array substrate ARand the counter-substrate CT, and is disposed between the firstalignment film AL1 and second alignment film AL2.

A first optical element OD1, which includes, e.g. a first polarizer PL1,is disposed on an outer surface 10B of the first insulative substrate 10which constitutes the array substrate AR. The first optical element OD1is located on that side of the liquid crystal display panel LPN, whichis opposed to the backlight 4, and controls the polarization state ofincident light which enters the liquid crystal display panel LPN fromthe backlight 4. A second optical element OD2, which includes, e.g. asecond polarizer PL2, is disposed on an outer surface 20B of the secondinsulative substrate 20 which constitutes the counter-substrate CT. Thesecond optical element OD2 is located on the display surface side of theliquid crystal display panel LPN, and controls the polarization state ofemission light emerging from the liquid crystal display panel LPN.

According to the above-described structure, when light emitted from thebacklight 4 has passed through the liquid crystal display panel LPN,transmissive light traveling through the first pixel electrode PE1 viathe first color filter CF1 is colored in blue (B), transmissive lighttraveling through the second pixel electrode PE2 via the second colorfilter CF2 is colored in green (G), and transmissive light travelingthrough the third pixel electrode PE3 via the third color filter CF3 iscolored in red (R). That part of the light, which has not passed throughthe first color filter CF1, second color filter CF2 and third colorfilter CF3, is almost entirely reflected, sent back to the backlight 4,and re-used. Specifically, the backlight 4 has a high-reflectancesurface which covers the light source, etc, and the reflective lightreflected toward the backlight 4 is then reflected once again toward theliquid crystal display panel LPN, with little light loss at thehigh-reflectance surface. Thus, the reflective light from the firstcolor filter CF1, second color filter CF2 and third color filter CF3 isre-used, and the efficiency of use of light is improved.

Next, more concrete structure examples of the first color filter CF1,second color filter CF2 and third color filter CF3 are described.

FIG. 4 is a cross-sectional view which schematically shows a dielectricfilm multilayer 41 with a 5-layer structure, which constitutes the firstcolor filter CF1, second color filter CF2 and third color filter CF3.

Specifically, the dielectric film multilayer 41 is composed of a firstsilicon nitride layer 311 which is disposed on the inner surface 10A ofthe first insulative substrate 10; a first silicon oxide layer 312stacked on the first silicon nitride layer 311; a second silicon nitridelayer 33 stacked on the first silicon oxide layer 312; a second siliconoxide layer 321 stacked on the second silicon nitride layer 33; and athird silicon nitride layer 322 stacked on the second silicon oxidelayer 321.

The first silicon nitride layer 311 and first silicon oxide layer 312function as the first semi-transmissive layer 31. The second siliconnitride layer 33 functions as the transmissive layer 33. The secondsilicon oxide layer 321 and third silicon nitride layer 322 function asthe second semi-transmissive layer 32. Specifically, each of the firstsemi-transmissive layer 31 and second semi-transmissive layer 32 is adielectric multilayer of two layers.

The first insulative substrate 10 is a glass substrate, and therefractive index thereof in the visible light wavelength range is about1.5. The first silicon nitride layer 311, second silicon nitride layer33 and third silicon nitride layer 322 are formed of, e.g. SiN, and therefractive index thereof in the visible light wavelength range is about2.0 to 2.7. Specifically, the first silicon nitride layer 311, secondsilicon nitride layer 33 and third silicon nitride layer 322 function ashigh-refractive-index layers having a higher refractive index than thefirst insulative substrate 10. The first silicon oxide layer 312 andsecond silicon oxide layer 321 are formed of, e.g. SiO₂, and therefractive index thereof in the visible light wavelength range is about1.5. Specifically, the first silicon oxide layer 312 and second siliconoxide layer 321 function as low-refractive-index layers having a lowerrefractive index than the high-refractive-index layers.

The first silicon nitride layer 311 and third silicon nitride layer 322have the same thickness, for example, 60 nm, in each of the first colorfilter CF1, second color filter CF2 and third color filter CF3. Thefirst silicon oxide layer 312 and second silicon oxide layer 321 havethe same thickness, for example, 90 nm, in each of the first colorfilter CF1, second color filter CF2 and third color filter CF3.Specifically, the low-refractive-index layers, which constitute thefirst semi-transmissive layer 31 and second semi-transmissive layer 32,are thicker than the high-refractive-index layers.

The second silicon nitride layer 33 has different film thicknesses inthe first color filter CF1, second color filter CF2 and third colorfilter CF3, respectively. For example, the thickness of the secondsilicon nitride layer 33 in the first color filter CF1 is about 85 nm,the thickness of the second silicon nitride layer 33 in the second colorfilter CF2 is about 115 nm, and the thickness of the second siliconnitride layer 33 in the third color filter CF3 is about 150 nm.

The first color filter CF1, which is composed of the dielectric filmmultilayer 41 having the above-described structure, has a transmittancepeak in the neighborhood of 470 nm, and has a reflectance bottom in theneighborhood of the same wavelength. Similarly, the second color filterCF2 has a transmittance peak in the neighborhood of 540 nm, and has areflectance bottom in the neighborhood of the same wavelength. Likewise,the third color filter CF3 has a transmittance peak in the neighborhoodof 610 nm, and has a reflectance bottom in the neighborhood of the samewavelength, while having a high reflectance in the wavelength rangeother than this wavelength.

The third silicon nitride layer 322 of the second color filter CF2 orthird color filter CF3 serves as an underlayer of the siliconsemiconductor layer. The silicon semiconductor layer has a high lightabsorption coefficient at short wavelengths. On the other hand, thebacklight, which is combined with the liquid crystal display panel, hassuch a light emission spectrum that the light intensity at relativelyshort wavelengths is high. As described above, since the second colorfilter CF2 or third color filter CF3, which is disposed under thesilicon semiconductor layer, has a relatively high reflectance in thewavelength range of short wavelengths, this second color filter CF2 orthird color filter CF3 can suppress light absorption in the siliconsemiconductor layer. Accordingly, in the switching element includingthis silicon semiconductor layer, photo-leakage current can be reduced.Thereby, the occurrence of crosstalk or flicker can be suppressed, and aliquid crystal display device with a good display quality can beprovided.

FIG. 5 is a cross-sectional view which schematically shows a dielectricfilm multilayer 42 with a 7-layer structure, which constitutes the firstcolor filter CF1, second color filter CF2 and third color filter CF3.

Specifically, the dielectric film multilayer 42 is composed of a firstsilicon nitride layer 311 which is disposed on the inner surface 10A ofthe first insulative substrate 10; a first silicon oxide layer 312stacked on the first silicon nitride layer 311; a second silicon nitridelayer 313 stacked on the first silicon oxide layer 312; a second siliconoxide layer 33 stacked on the second silicon nitride layer 313; a thirdsilicon nitride layer 321 stacked on the second silicon oxide layer 33;a third silicon oxide layer 322 stacked on the third silicon nitridelayer 321; and a fourth silicon nitride layer 323 stacked on the thirdsilicon oxide layer 322.

The first silicon nitride layer 311, first silicon oxide layer 312 andsecond silicon nitride layer 313 function as the first semi-transmissivelayer 31. The second silicon oxide layer 33 functions as thetransmissive layer 33. The third silicon nitride layer 321, thirdsilicon oxide layer 322 and fourth silicon nitride layer 323 function asthe second semi-transmissive layer 32. Specifically, each of the firstsemi-transmissive layer 31 and second semi-transmissive layer 32 is adielectric multilayer of three layers.

The first silicon nitride layer 311, second silicon nitride layer 313,third silicon nitride layer 321 and fourth silicon nitride layer 323 areformed of, e.g. SiN, and function as high-refractive-index layers (therefractive index in the visible light wavelength range is about 2.0 to2.7). The first silicon oxide layer 312, second silicon oxide layer 33and third silicon oxide layer 322 are formed of, e.g. SiO₂, and functionas low-refractive-index layers (the refractive index in the visiblelight wavelength range is about 1.5).

The first silicon nitride layer 311, second silicon nitride layer 313,third silicon nitride layer 321 and fourth silicon nitride layer 323have the same thickness, for example, 60 nm, in each of the first colorfilter CF1, second color filter CF2 and third color filter CF3. Thefirst silicon oxide layer 312 and third silicon oxide layer 322 have thesame thickness, for example, 90 nm, in each of the first color filterCF1, second color filter CF2 and third color filter CF3.

The second silicon oxide layer 33 has different film thicknesses in thefirst color filter CF1, second color filter CF2 and third color filterCF3, respectively. For example, the thickness of the second siliconoxide layer 33 in the first color filter CF1 is about 130 nm, thethickness of the second silicon oxide layer 33 in the second colorfilter CF2 is about 180 nm, and the thickness of the second siliconoxide layer 33 in the third color filter CF3 is about 30 nm.

The fourth silicon nitride layer 323 of the second color filter CF2 orthird color filter CF3 serves as an underlayer of the siliconsemiconductor layer.

The first color filter CF1, which is formed of the dielectric filmmultilayer 42 having the above-described structure, has a transmittancepeak and a reflectance bottom in the neighborhood of 470 nm. Inaddition, in this first color filter CF1, compared to the first colorfiler CF1 that is formed of the dielectric film multilayer 41, thewavelength range in the neighborhood of the transmittance peak andreflectance bottom becomes narrower, and the wavelength range of a highreflectance becomes wider. Similarly, the second color filter CF2, whichis formed of the dielectric film multilayer 42, has a transmittance peakand a reflectance bottom in the neighborhood of 540 nm. In addition, inthis second color filter CF2, compared to the second color filer CF2that is formed of the dielectric film multilayer 41, the wavelengthrange in the neighborhood of the transmittance peak and reflectancebottom becomes narrower, and the wavelength range of a high reflectancebecomes wider. Likewise, the third color filter CF3, which is formed ofthe dielectric film multilayer 42, has a transmittance peak and areflectance bottom in the neighborhood of 610 nm. In addition, in thisthird color filter CF3, compared to the third color filer CF3 that isformed of the dielectric film multilayer 41, the wavelength range in theneighborhood of the transmittance peak and reflectance bottom becomesnarrower, and the wavelength range of a high reflectance becomes wider.

As has been described above, by increasing the number of layers of thedielectric film multilayer, the wavelength range in the neighborhood ofthe transmittance peak becomes narrower. Therefore, the color purity ofeach of the first color filter CF1, second color filter CF2 and thirdcolor filter CF3 can be improved. In addition, since the wavelengthrange of the high reflectance of the second color filter CF2 or thirdcolor filter CF3, which is disposed under the silicon semiconductorlayer, becomes wider, this second color filter CF2 or third color filterCF3 can further suppress light absorption in the silicon semiconductorlayer. Thus, a liquid crystal display device with a good display qualitycan be provided.

FIG. 6 is a cross-sectional view which schematically shows a dielectricfilm multilayer 43 with a 9-layer structure, which constitutes the firstcolor filter CF1, second color filter CF2 and third color filter CF3.

Specifically, the dielectric film multilayer 43 is composed of a firstsilicon nitride layer 311 which is disposed on the inner surface 10A ofthe first insulative substrate 10; a first silicon oxide layer 312stacked on the first silicon nitride layer 311; a second silicon nitridelayer 313 stacked on the first silicon oxide layer 312; a second siliconoxide layer 314 stacked on the second silicon nitride layer 313; a thirdsilicon nitride layer 33 stacked on the second silicon oxide layer 314;a third silicon oxide layer 321 stacked on the third silicon nitridelayer 33; a fourth silicon nitride layer 322 stacked on the thirdsilicon oxide layer 321; a fourth silicon oxide layer 323 stacked on thefourth silicon nitride layer 322; and a fifth silicon nitride layer 324stacked on the fourth silicon oxide layer 323.

The first silicon nitride layer 311, first silicon oxide layer 312,second silicon nitride layer 313 and second silicon oxide layer 314function as the first semi-transmissive layer 31. The third siliconnitride layer 33 functions as the transmissive layer 33. The thirdsilicon oxide layer 321, fourth silicon nitride layer 322, fourthsilicon oxide layer 323 and fifth silicon nitride layer 324 function asthe second semi-transmissive layer 32. Specifically, each of the firstsemi-transmissive layer 31 and second semi-transmissive layer 32 is adielectric multilayer of four layers.

The first silicon nitride layer 311, second silicon nitride layer 313,third silicon nitride layer 33, fourth silicon nitride layer 322 andfifth silicon nitride layer 324 are formed of, e.g. SiN, and function ashigh-refractive-index layers (the refractive index in the visible lightwavelength range is about 2.0 to 2.7). The first silicon oxide layer312, second silicon oxide layer 314, third silicon oxide layer 321 andfourth silicon oxide layer 323 are formed of, e.g. SiO₂, and function aslow-refractive-index layers (the refractive index in the visible lightwavelength range is about 1.5).

The first silicon nitride layer 311, second silicon nitride layer 313,fourth silicon nitride layer 322 and fifth silicon nitride layer 324have the same thickness, for example, 60 nm, in each of the first colorfilter CF1, second color filter CF2 and third color filter CF3. Thefirst silicon oxide layer 312, second silicon oxide layer 314, thirdsilicon oxide layer 321 and fourth silicon oxide layer 323 have the samethickness, for example, 90 nm, in each of the first color filter CF1,second color filter CF2 and third color filter CF3.

The third silicon nitride layer 33 has different film thicknesses in thefirst color filter CF1, second color filter CF2 and third color filterCF3, respectively. For example, the thickness of the third siliconnitride layer 33 in the first color filter CF1 is about 80 nm, thethickness of the third silicon nitride layer 33 in the second colorfilter CF2 is about 115 nm, and the thickness of the third siliconnitride layer 33 in the third color filter CF3 is about 30 nm.

The fifth silicon nitride layer 324 of the second color filter CF2 orthird color filter CF3 serves as an underlayer of the siliconsemiconductor layer.

The first color filter CF1, which is formed of the dielectric filmmultilayer 43 having the above-described structure, has a transmittancepeak and a reflectance bottom in the neighborhood of 470 nm. Inaddition, in this first color filter CF1, compared to the first colorfiler CF1 that is formed of the dielectric film multilayer 42, thewavelength range in the neighborhood of the transmittance peak andreflectance bottom becomes narrower, and the wavelength range of a highreflectance becomes wider. Similarly, the second color filter CF2, whichis formed of the dielectric film multilayer 43, has a transmittance peakand a reflectance bottom in the neighborhood of 540 nm. In addition, inthis second color filter CF2, compared to the second color filer CF2that is formed of the dielectric film multilayer 42, the wavelengthrange in the neighborhood of the transmittance peak and reflectancebottom becomes narrower, and the wavelength range of a high reflectancebecomes wider. Likewise, the third color filter CF3, which is formed ofthe dielectric film multilayer 43, has a transmittance peak and areflectance bottom in the neighborhood of 610 nm. In addition, in thisthird color filter CF3, compared to the third color filer CF3 that isformed of the dielectric film multilayer 42, the wavelength range in theneighborhood of the transmittance peak and reflectance bottom becomesnarrower, and the wavelength range of a high reflectance becomes wider.

Thus, the color purity of each of the first color filter CF1, secondcolor filter CF2 and third color filter CF3 can further be improved. Inaddition, the light absorption in the silicon semiconductor layer canfurther be suppressed. Therefore, a liquid crystal display device with agood display quality can be provided.

In the meantime, the position of the reflectance bottom of thereflection spectrum or the position of the transmittance peak of thetransmission spectrum, in each of the first color filter CF1, secondcolor filter CF2 and third color filter CF3, can be adjusted by varyingthe film thickness of the transmissive layer 33. The number of layersand the thickness of the transmissive layer can be determined, whiletaking into account the capabilities which are required in the firstcolor filter CF1, second color filter CF2 and third color filter CF3,and the photo-leakage resistance.

FIG. 7 is a graph showing an example of the relationship between thelight emission spectrum of the backlight 4 and the reflection spectra ofthe color filters of the embodiment. In FIG. 7, the abscissa indicateswavelength (nm) and the ordinate indicates the light intensity of thebacklight 4 and the reflectance of the color filter. The light intensityand the reflectance are relative values in the case where the maximumvalue is set at 1.

The reflection spectra of the color filters, which are shown in FIG. 7,were obtained by calculating the reflectance on the first insulativesubstrate 10 side of the incident light from the first insulativesubstrate 10, with respect to a model which is fabricated in thefollowing manner. A third color filter CF3 is disposed on the firstinsulative substrate. A polysilicon semiconductor layer with a thicknessof 50 nm of a switching element is disposed on the third color filterCF3. This polysilicon semiconductor layer is covered with a firstinsulation film (gate insulation film) 11 with a thickness of 80 nm,which is formed of silicon oxide (SiO). A gate electrode with athickness of 300 nm, which is formed of molybdenum (Mo), is disposed onthe first insulation film.

In FIG. 7, “BL intensity” is a light emission spectrum of the backlight4. FIG. 7 shows reflection spectra in a case (corresponding to “TFT on5-layer CF3” in FIG. 7) where the dielectric film multilayer 41 of the5-layer structure shown in FIG. 4 was applied to the structure of thethird color filter CF3, a case where (“TFT on 7-layer CF3”) where thedielectric film multilayer 42 of the 7-layer structure shown in FIG. 5was applied to the structure of the third color filter CF3, and a casewhere (“TFT on 9-layer CF3”) where the dielectric film multilayer 43 ofthe 9-layer structure shown in FIG. 6 was applied to the structure ofthe third color filter CF3. FIG. 7 shows, as a comparative example, areflection spectrum in a case (corresponding to “TFT/UC” in FIG. 7)where only an undercoat layer (SiN/SiO), in place of the third colorfilter, was disposed under the switching element.

As shown in FIG. 7, the light emission spectrum of the backlight 4 has alight emission peak in the neighborhood of 450 nm. By contrast, in thereflection spectrum of “TFT/UC” of the comparative example, it isunderstood that the reflectance at the wavelength of 450 nm is very low.On the other hand, the reflectance spectrum of “TFT on 5-layer CF3” ofthe embodiment has a reflectance of about 50% in the neighborhood of 450nm. In addition, the reflectance spectrum of “TFT on 7-layer CF3” has areflectance of about 70% in the neighborhood of 450 nm. Besides, thereflectance spectrum of “TFT on 9-layer CF3” has a reflectance of about80% in the neighborhood of 450 nm. It was thus confirmed that thereflectance of light in the neighborhood of a specific wavelength (450nm in this example) increases as the number of layers of the dielectricfilm multilayer becomes larger.

Although not illustrated, the inventor conducted similar calculations inthe case where the second color filter CF2 was disposed under theswitching element, and confirmed that the reflectance of 50% or more wasobtained in the neighborhood of 450 nm, and that the reflectance oflight in the neighborhood of a specific wavelength increases as thenumber of layers of the dielectric film multilayer, which constitutesthe second color filter CF2, becomes larger.

FIG. 8 is a graph showing the relationship between the photo-leakageamount in the switching element of each of pixels and the number oflayers of the dielectric film multilayer. In FIG. 8, the abscissaindicates the number of layers of the dielectric film multilayer (thirdcolor filter CF3) which is disposed under the switching element, and theordinate indicates a ratio of a photo-leakage amount in the case wherethe photo-leakage amount at a time when only the undercoat layer(SiN/SiO), in place of the third color filter, was disposed under theswitching element, is set at 1.

It was confirmed that the photo-leakage amount is about 65% when theswitching element is disposed on the third color filter CF3 which iscomposed of the dielectric film multilayer 41 of the 5-layer structure.It was confirmed that the photo-leakage amount is about 45% when theswitching element is disposed on the third color filter CF3 which iscomposed of the dielectric film multilayer 42 of the 7-layer structure.It was confirmed that the photo-leakage amount is about 40% when theswitching element is disposed on the third color filter CF3 which iscomposed of the dielectric film multilayer 43 of the 9-layer structure.

The SiN layers, which are used as high-refractive-index layers in the5-layer structure, 7-layer structure and 9-layer structure, are formedby plasma CVD using SiH₄ and NH₃ as a principal material gas, under thecondition that the in-film hydrogen amount may become 2×10²¹ cm⁻³ ormore. In order to obtain a film of a high refractive index, it can bethought that a silicon nitride (SiN) film is formed by, e.g. sputtering.In general, the in-film hydrogen amount in a SiN film that is formed bysputtering is very low. By using an SiN film containing hydrogen, thecharacteristics of a top-gate-type thin-film transistor, which serves aswitching element, can be improved. For example, when polysilicon wasused for the silicon semiconductor SC of the switching element, thethreshold voltage of the thin-film transistor, in the case where thecolor filter layer was formed of a multiplayer of silicon nitride filmsand silicon oxide films formed by sputtering, was 5.0 V on average. Onthe other hand, the threshold voltage of the thin-film transistor, inthe case where the color filter layer was formed of a multiplayer ofsilicon nitride films and silicon oxide films formed by plasma CVD withan in-film hydrogen amount of 2×10²¹ cm⁻³ or more, decreased to 2.1 V.Thereby, the active matrix circuit can be driven with a low voltage,contributing to reduction in power consumption.

As has been described above, according to the present embodiment, aliquid crystal display device which has a good display quality can beprovided.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A liquid crystal display device comprising anarray substrate comprising: a gate line; a first source line and asecond source line which cross the gate line; a first color filterconfigured to transmit light in a first wavelength range; a second colorfilter configured to transmit light in a second wavelength range ofgreater than the first wavelength range; a first switching elementelectrically connected to the gate line and the first source line; asecond switching element electrically connected to the gate line and thesecond source line; a first pixel electrode which is electricallyconnected to the first switching element and is located to overlap withthe first color filter; and a second pixel electrode which iselectrically connected to the second switching element and is located tooverlap with the second color filter, wherein the first switchingelement includes a first gate electrode, a first semiconductor layer,and a first region at which the first gate electrode and the firstsemiconductor layer is overlapped, the second switching element includesa second gate electrode, a second semiconductor layer, and a secondregion at which the second gate electrode and the second semiconductorlayer is overlapped, and the first region and the second region areoverlapped with the second color filter.
 2. The liquid crystal displaydevice of claim 1, wherein the first wavelength range is a bluewavelength range.
 3. The liquid crystal display device of claim 1,further comprising a backlight located on a back side of the arraysubstrate, wherein a light emission spectrum of the backlight has alight emission peak at least in the first wavelength range.
 4. Theliquid crystal display device of claim 1, wherein the firstsemiconductor layer and the second semiconductor layer are formed ofpolysilicon or amorphous silicon.
 5. A liquid crystal display devicecomprising an array substrate comprising: a gate line; a first sourceline and a second source line which cross the gate line; a first colorfilter configured to transmit light in a first wavelength range; asecond color filter configured to transmit light in a second wavelengthrange of greater than the first wavelength range; a first switchingelement electrically connected to the gate line and the first sourceline; a second switching element electrically connected to the gate lineand the second source line; a first pixel electrode which iselectrically connected to the first switching element and is located tooverlap with the first color filter; and a second pixel electrode whichis electrically connected to the second switching element and is locatedto overlap with the second color filter, wherein the first switchingelement includes a first gate electrode, a first semiconductor layer,and a first region at which the first gate electrode and the firstsemiconductor layer is overlapped, the second switching element includesa second gate electrode, a second semiconductor layer, and a secondregion at which the second gate electrode and the second semiconductorlayer is overlapped, the first region is located between the first gateelectrode and the second color filter, and the second region is locatedbetween the second gate electrode and the second color filter.
 6. Theliquid crystal display device of claim 5, wherein the first wavelengthrange is a blue wavelength range.
 7. The liquid crystal display deviceof claim 5, further comprising a backlight located on a back side of thearray substrate, wherein a light emission spectrum of the backlight hasa light emission peak at least in the first wavelength range.
 8. Theliquid crystal display device of claim 5, wherein the firstsemiconductor layer and the second semiconductor layer are formed ofpolysilicon or amorphous silicon.
 9. A liquid crystal display devicecomprising an array substrate comprising: a gate line; a first sourceline and a second source line which cross the gate line; a first pixelwhich displays a first color; and a second pixel which displays a secondcolor different from the first color; wherein the first pixel includes afirst color filter with a first film thickness, a second color filterwith a second film thickness which is different from the first filmthickness, a first switching element which is electrically connected tothe gate line and the first source line, and a first pixel electrodewhich is electrically connected to the first switching element and islocated to overlap with the first color filter, the first switchingelement includes a first gate electrode, a first semiconductor layer,and a first region at which the first gate electrode and the firstsemiconductor layer is overlapped, the first region is overlapped withthe second color filter, the first color filter is configured totransmit the first color, the second color filter is configured totransmit a third color which is different from the first color and thesecond color, the second pixel includes a third color filter with athird film thickness which is different from the first film thicknessand the second film thickness, a fourth color filter with the secondfilm thickness, a second switching element which is electricallyconnected to the gate line and the second source line, and a secondpixel electrode which is electrically connected to the second switchingelement and is located to overlap with the third color filter, thesecond switching element includes a second gate electrode, a secondsemiconductor layer, and a second region at which the second gateelectrode and the second semiconductor layer is overlapped, the secondregion is overlapped with the fourth color filter, the third colorfilter is configured to transmit the second color, and the fourth colorfilter is configured to transmit the third color.
 10. The liquid crystaldisplay device of claim 9, wherein the first color is blue.
 11. Theliquid crystal display device of claim 9, further comprising a backlightlocated on a back side of the array substrate, wherein a light emissionspectrum of the backlight has a light emission peak at least in thefirst color.
 12. The liquid crystal display device of claim 9, whereinthe first semiconductor layer and the second semiconductor layer areformed of polysilicon or amorphous silicon.